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PC is killing Power Supplies


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#1 dinkey79

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Posted 29 September 2015 - 01:13 PM

I've got a Dell Optiplex 745 Tower. Power supply failed so installed a new one and got the same results tried two others and finally realized that the power supply was good, tested good with testers but after placing them in the PC and hitting power button they are no longer good. Power supply tester only shows one green light +5vsb all the rest are dark. What might be causing this?



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#2 Pentodes

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Posted 29 September 2015 - 07:38 PM

I'm a little confused here, the power supplies test OK  but not when connected to the mobo or does it 'blow' the power supply?

 

But hang on, so we don't have egg on our faces, disconnect ALL USB leads, they use the 5V rail and draw power.... now if one of them was faulty ?

 

What next, well a good look round the mobo looking at electrolytic capacitors, these look like little 'metal cans', they do and can become faulty, when they do they usually swell up, their tops become 'domed' rather than flat, sometimes they leak gunge which can eat through the protective lacquer on the mobo and gobble all the copper tracks underneath.... then what to do next ?

 

I would be disconnecting everything all usb leads including all drives, yes remove the hard drives as well..... except the power leads to the mobo and fans fans, so we end up with the mobo, RAM and CPU, power supply  and monitor connected.... sounds crazy uh? ..... but the mobo should boot or to be more exact POST (Power On Self Test) AND the monitor will display - 'No Hard drive found', 'insert the disc with the operating system on' or something, the exact wording really depends on who programed the bios..... now then this tells us the mobo is working, some mobos give a bleep when it POST- if you reboot you should be able to get into the bios set up screen if you wished, this is irrelevant at this stage though.

 

If the mobo don't boot and you can't see any warning on the monitor we're looking at either the mobo, CPU or ram fault.

 

Should you be able to boot (POST), you'll  see a warning on the monitor, the thing to do now is add one item back at a time and keep rebooting, could be a hard drive, could be a dvd drive or whatever has been disconnected.

 

We boot an hard drive, cos we gotta get the motor running to spin the disc to get the data and 'wake' (POST) the Bios to kick the mobo out of bed, but folks still say 'boot the bios', even me.

 

Dave


Edited by Pentodes, 29 September 2015 - 07:41 PM.


#3 dinkey79

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Posted 19 October 2015 - 10:18 AM

Finally just changed the motherboard out and everything worked great.  Thanks for your help.






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